This invention relates to a spool valve having throttling slots which are required to be in alignment with certain ports in the encompassing housing. This results in a requirement to prevent rotation of the valve spool within the housing. The invention relates in particular to a valve spool which fulfills the above criteria and which is pilot operated.
Spool valves which are manufactured with throttling slots in the spool thereof to communicate a groove in the housing with the next adjacent groove under controlled conditions are well known in the art. Generally the grooves in the housing are annular and spool alignment is not critical. Certain spool valves are constructed with throttling grooves which require alignment with ports communicating with a land in the bore of the valve rather than with a groove defined in the bore. Valve spools of the configuration just described are known to be manually controlled by means of a linkage which prevents rotation of the valve spool in the housing thus maintaining the critical alignment. In certain applications it has been found desirable to operate this same valve not by a control lever but by pilot pressure from a remote location.
Normally pilot operated valves are constructed with a cylindrical shaped pilot chamber wherein the pilot fluid is applied against one end or the other end of the valve spool to urge the spool in desired direction. Generally if the spool rotates during reciprocation in the associated housing, no undesirable results occur. However, in the present situation rotation must be prevented. To extend a noncircular portion of the valving spool into a pilot chamber and further to seal the pilot chamber against leakage proves difficult in view of the noncircular nature of the opening due to the inherent problem of machining noncircular openings. This machining problem coupled with the necessity for close tolerances and providing for seal means in the pilot chamber to prevent leakage, makes the problem more difficult. To add an actuator motor to the control lever of manually controlled valves, although providing a satisfactory solution, unduly complicates the problem and adds weight to the associated machinery.